http://gamemakerblog.com/2013/11/25/gamemaker-studio-standard-edition-is-currently-free-50-value/
Download, install, and let it update.
Edit: A poster mentioned you need to select the “Beta” update option (you’ll see it) to get the option for the free license. That’s the option I picked.
The program will restart and launch with a window with three options: one to use the *free* (feature-gimped) version, one to register for a free studio license, and one to enter a studio license.
It’s the second option. Enter your email. Enter it again, hit register. Key comes to you. Enter the key. VOILA.
Originally published at The Scotto Grotto. You can comment here or there.